70 IMPROVEMENT OF THE SOIL BY 



which are evolved from animal or vegetable substances 

 while undergoing fermentation ; — and, secondly, to ren- 

 der soluble, or available as the food of plants, matters 

 which are not already so, as swamp earth, woody jfibre, 

 &c. There is nothing added to the elements of fertility 

 by mixing organic with inorganic matters in a compost- 

 heap. The advantage in one case is m saving that which 

 would otherwise be lost ; and in the other, of rendering 

 useful that which is otherwise useless. Earthy matters 

 absorb and retain the fertilizing properties of liquids and 

 gases, if placed in juxtaposition, or in contact with them, 

 and impart them again to growing plants. Thus a fer- 

 menting dung-heap will enrich the stratum of earth with 

 which it is covered, by the gases which it gives off; thus 

 the earthy matters with which we bed our cattle-yards 

 become rich in the elements of fertility, by the urine and 

 juices of the dung which they there imbibe ; and "thus the 

 inert, insoluble matter of peat-swamps is rendered soluble 

 and enriching, by bringing it in contact with recent ma- 

 nure, or other heating and fermenting substance. It is 

 the business of the farmer to calculate, upon the foregoing 

 principles, and upon the proximity and cost of the mate- 

 rials, to what extent composts may be made profitable in 

 the economy of the farm. To some they are highly use- 

 ful ; while to others, hke Franklin's whistle, they may 

 cost too dear. 



There are several other animal and vegetable sub- 

 stances, which every farmer has more or less at com- 

 mand, or which he may have at command, besides his 

 cattle-dung, which may be made to contribute largely and 

 economically, to keep up and increase the fertility and 

 products of his lands. We will notice some of them 

 briefly in detail. 



1. Bone-dust^ or crushed bones. The bones of the 

 ox, according to Davy, consist of 51 parts in 100 of 

 decomposable animal matter, 37 of phosphate of lime, 10 

 of carbonate of lime, and 1.3 of phosphate of magnesia. 

 All these matters impart fertility, and are necessary ele- 

 ments in the food of plants. They are species of con- 

 centrated, or portable manure : concentrated^ inasmuch 



